a A (ligand)2-Cu complex was prepared using BuLi and CuCl2, and used as 1 mol % (relative to EDA) in dichloroethane, at 25 °C, styrene to EDA ratio ) 3:1. Before the addition of EDA, the complex was activated with phenylhydrazine. b 1 mol % ligand-Cu(OTf) complex (relative to EDA) in CHCl3, at 25 °C, styrene to EDA ratio ) 5:1. c n.g. ) not given. Scheme 3. Proposed Cyclopropanation Mechanism a a Refs 10, 18-20. Chart 2. The Proposed Transition State in the Cyclopropanation ReactionsEnantiocontrol Aspects a a R1, R2 ) Ph, H or H, Ph. 14
[reaction: see text] We report here the first heterogenization of a bis(oxazoline) ligand on an inorganic (silica) surface. The activity and enantioselectivity of this new material as a catalyst for the Diels-Alder reaction were checked, and it was shown that under certain conditions enantioselectivities similar to those of the homogeneous catalyst are reached. It was also shown that under these conditions the catalyst can be recycled without loss of activity or selectivity.
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